1. Field of the Invention
The present invention relates to a semiconductor memory device and an operation method thereof.
2. Description of the Related Art
Various devices have become compatible with the memory card in these years. For example, the memory card is used for cellular phones to store camera-taken images, music, and video, backup of built-in memory, and the like. And, the memory card is being made to have a larger capacity. An 32-GB memory card having a capacity larger than that of DVD is already on the market, and the memory card is being advanced to have larger capacities. The large-capacity memory card stores various kinds of user data (for example, personally shot image data, copyright-protected music and video data, and personal information).
Formatting is generally used to erase all user data in the memory card. The formatting includes full formatting and quick formatting. The full formatting erases the whole user data in the memory card. Meanwhile, the quick formatting erases data of an area (for example, FAT1 area) managing the file system of the user data to disable the access to the user data. As a result, there is provided the same effect as the erase of the user data itself.
Since the full formatting of a large capacity memory card requires a considerable time, the quick formatting is usually used, and the users also often select the quick formatting. And, there is also a host device which is compatible with quick formatting only.
According to the quick formatting, the user data can be read because the user data itself is remained in the memory card. For example, there is commercially available software which restores the erased data if data in the memory card is accidentally erased.
SSD (Solid State Drive), in which a hard disc is replaced with NAND type flash memories, has been developing as new memory devices.
In order to prevent data that is recorded on a recording medium from unwanted outflow, there is disclosed a technology of recording data by encrypting the data, performing address conversion of a designated address, and recording the data by using the converted address (JP-A No. 2004-152440).
Even if the data is encrypted, however, the data might be decoded by analyzing the encrypted data if the data could be fetched as it was.